I experience no indicating on roundabouts quite often, I wish people would exert that little bit of energy and hit the indicator, it would speed up things at roundabouts so much...
I've also recently experienced quite a few people pulling out at me on roundabouts. It was a bus last weekend, and this weekend I had a young girl pull out on a roundabout in front of me... The girl was easier to spot, it was a more open roundabout, but she had stopped, and I saw her as I entered the roundabout (not indicating as I was going straight on/taking second exit), and I assumed something wasn't quite right as she started moving again... That sort of set off a wee alarm bell in my head saying something's wrong, maybe I should hit the brakes, and my instincts were right

She pulled out in front, accelerating very slowly... I noticed she had R plates up, and I just let her go on, putting it down to her inexperience... I think it might be something to do with the small car or something, people don't think you'll be going at any speed...
On this occasion I didn't indicate my exit from the roundabout, I was too busy with changing gear to get away from the roundabout as soon as possible, and my instructor told me that if there is a situation when you need to change gear and indicate at the same time, it's better to change gear and forget the indicator, but I still felt a bit bad...
What about a time like that, would it be permissable to not indicate?